This invention relates to a fluid operated damper unit. Fluid operated damper units as considered by the present invention may be used for damping relative movement of two constructional parts in a mechanical construction; more particularly, such a fluid operated damper unit may be used in combination with a linear driving unit which is used for performing relative movement of said constructional parts. In such a combination, it is sometimes desirable that the relative movement of the constructional parts is damped when approaching both ends of a respective path of relative movement, whereas in a respectively preceding section of said path of movement, the damping effect is reduced or zero, this behaviour being true for both directions of relative movement. An example for such a situation are gear boxes of modern vehicles and more particularly, trucks. In such gear boxes, a pneumatic or hydraulic positioning device of the cylinder piston type is used for providing a desired gear ratio by movement of a gear wheel. The positioning device is movable in opposite directions. After a first phase of movement of the positioning device, a synchronization is obtained. After the synchronization has been obtained, the positioning device continues its movement in the same direction until the desired transmission ratio has been finally reached. This is true for both directions of movement.
In such an application it is desirable that for both directions of movement the positioning device moves during the first phase, i.e. from a respective terminal position, as quickly as possible and at minimum energy consumption, until the synchronization is initiated. Hereupon, a damped further movement of the positioning device is desired.